U.S. patent application number 11/003384 was filed with the patent office on 2005-06-09 for decoupling capacitors and semiconductor integrated circuit.
This patent application is currently assigned to MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.. Invention is credited to Tsutsumi, Masanori, Yano, Junichi.
Application Number | 20050122755 11/003384 |
Document ID | / |
Family ID | 34631802 |
Filed Date | 2005-06-09 |
United States Patent
Application |
20050122755 |
Kind Code |
A1 |
Tsutsumi, Masanori ; et
al. |
June 9, 2005 |
Decoupling capacitors and semiconductor integrated circuit
Abstract
VSS 302 is provided to a gate portion 304 and VDD 301 is
provided to a source portion 305 and a drain portion 306 of a MOS
transistor which constitutes a decoupling capacitor, and a
potential NWVDD 303 different from that provided to the source
portion 305 and the drain portion 306 is provided to a substrate
portion 307. If NWVDD 303 is set higher than VDD 301, a depletion
layer 309 is spread, so that a leakage current can be reduced
instead of reducing a capacitance of the decoupling capacitor. In
addition, if NWVDD 303 is set lower than VDD 301 so as not to cause
latchup, the depletion layer 309 is reduced, so that the
capacitance of the decoupling capacitor can be increased. By
changing the potential NWVDD 303 provided to the substrate portion
307, a capacitance value and a leakage current value of the
decoupling capacitor can be controlled. Thereby making it possible
to achieve a decoupling capacitor capable of controlling the
capacitance value and the leakage current value and also having
excellent response characteristics.
Inventors: |
Tsutsumi, Masanori;
(Souraku-gun, JP) ; Yano, Junichi; (Ibaraki-shi,
JP) |
Correspondence
Address: |
STEVENS DAVIS MILLER & MOSHER, LLP
1615 L STREET, NW
SUITE 850
WASHINGTON
DC
20036
US
|
Assignee: |
MATSUSHITA ELECTRIC INDUSTRIAL CO.,
LTD.
Osaka
JP
|
Family ID: |
34631802 |
Appl. No.: |
11/003384 |
Filed: |
December 6, 2004 |
Current U.S.
Class: |
365/51 ;
257/E27.016; 257/E27.05 |
Current CPC
Class: |
H01L 27/0629 20130101;
H01L 27/0811 20130101 |
Class at
Publication: |
365/051 |
International
Class: |
G11C 005/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 8, 2003 |
JP |
2003-409173 |
Claims
What is claimed is:
1. A decoupling capacitor, comprising: a MOS transistor which has
source/drain regions of a second conductive type formed on a
surface of a substrate region of a first conductive type, wherein a
capacitance value of said decoupling capacitor is changed by
changing a potential of said substrate region.
2. The decoupling capacitor according to claim 1, wherein by
gradually changing the potential of said substrate region, the
capacitance value of said decoupling capacitor is gradually
changed.
3. A decoupling capacitor, comprising: a MOS transistor which has
source/drain regions of a second conductive type formed on a
surface of a substrate region of a first conductive type, wherein a
leakage current value of said decoupling capacitor is changed by
changing a potential of said substrate region.
4. The decoupling capacitor according to claim 3, wherein by
gradually changing the potential of said substrate region, the
leakage current value of said decoupling capacitor is gradually
changed.
5. A decoupling capacitor, comprising: a MOS transistor which has
source/drain regions of a second conductive type formed on a
surface of a substrate region of a first conductive type, wherein a
first interconnection connected to said substrate region and a
second interconnection connected to source/drain regions of said
MOS transistor are electrically isolated.
6. The decoupling capacitor according to claim 5, wherein different
potentials are provided to said first interconnection and said
second interconnection.
7. The decoupling capacitor according to claim 5, wherein the
potential provided to said first interconnection is changed by a
control signal.
8. A semiconductor integrated circuit, comprising: a plurality of
logic cells for constituting a logic comprising a MOS transistor
which has source/drain regions of a second conductive type formed
on a surface of a first substrate region of a first conductive
type, and a MOS transistor which has source/drain regions of the
first conductivity type formed on a surface of a second substrate
region of the second conductive type respectively; and a decoupling
capacitor comprising a MOS transistor which has source/drain
regions of the second conductive type formed on a surface of a
third substrate region of the first conductive type, wherein an
interconnection for providing a potential to said third substrate
region of said decoupling capacitor and an interconnection for
providing a potential to the source/drain regions of said MOS
transistor of said decoupling capacitor are electrically
isolated.
9. The semiconductor integrated circuit according to claim 8,
wherein said third substrate region is electrically isolated from
said first substrate region.
10. The semiconductor integrated circuit according to claim 8,
wherein a potential different from that provided to said first
substrate region is provided to said third substrate region.
11. The semiconductor integrated circuit according to claim 8,
wherein an interconnection for providing a potential to said first
substrate region of said logic cells and an interconnection for
providing a potential to the source region of said MOS transistor
which has source/drain regions of the second conductive type of
said logic cell are electrically isolated, wherein the potential
provided to said third substrate region of said decoupling
capacitor and the potential provided to said first substrate region
of said logic cell are controlled independently.
12. The semiconductor integrated circuit according to claim 8,
wherein said logic cell is placed in a plurality of cell rows, and
said decoupling capacitor is placed between the cell rows.
13. The semiconductor integrated circuit according to claim 8,
wherein said logic cell is placed in a plurality of cell rows, said
decoupling capacitor is placed in the cell rows and said third
substrate region of said decoupling capacitor is apart from a
boundary portion of said logic cell adjacent thereto.
14. The semiconductor integrated circuit according to claim 8,
wherein a potential of said third substrate region of said
decoupling capacitor is controlled according to an operating
frequency of said semiconductor integrated circuit.
15. The semiconductor integrated circuit according to claim 8,
wherein a capacitance value of said decoupling capacitor is
controlled according to the operating frequency of said
semiconductor integrated circuit.
16. The semiconductor integrated circuit according to claim 8,
wherein the potential of said third substrate region of said
decoupling capacitor is controlled according to an operation mode
of said semiconductor integrated circuit.
17. The semiconductor integrated circuit according to claim 8,
wherein the capacitance value of said decoupling capacitor is
controlled according to an operation mode of said semiconductor
integrated circuit.
18. The semiconductor integrated circuit according to claim 8,
wherein it further comprises a plurality of functional blocks
comprising a group of said logic cells, wherein said decoupling
capacitor is arranged in each of said functional blocks, and the
potential of said third substrate region of said decoupling
capacitor is controlled for every said functional block according
to the operation mode of said semiconductor integrated circuit.
19. The semiconductor integrated circuit according to claim 8,
wherein it further comprises a plurality of blocks comprising a
group of said logic cells, wherein said decoupling capacitor is
plced among said blocks.
20. The semiconductor integrated circuit according to claim 19,
wherein it further comprises a plurality of decoupling capacitors
placed among between said blocks, wherein respective substrate
potentials of said decoupling capacitors are controlled
independently.
21. The semiconductor integrated circuit according to claim 20,
wherein said decoupling capacitor is arranged also in each of said
blocks, and a potential of said third substrate region of at least
one decoupling capacitor among a plurality of decoupling capacitors
arranged between said blocks is controlled in conjunction with a
control of a potential of said third substrate region of a
decoupling capacitor arranged in either of said blocks.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a decoupling capacitor and
a semiconductor integrated circuit using the same.
[0003] 2. Description of Related Art
[0004] In recent years, along with improvement in speed and
advanced features of a digital circuit, an improvement in speed and
a high-density integration of a semiconductor integrated circuit
have been made progress. Power consumption of a chip has increased
due to the improvement in speed and the high-density integration of
the semiconductor integrated circuit and a supply voltage drop
(IR-DROP) has posed a problem in connection with it, and there have
arisen problems that switching speed of a transistor has been
decreased due to a supply voltage drop, resulting in a decrease in
operating frequency of a circuit, and noise margin has been
decreased due to the supply voltage drop and mislatch of data or
the like has been generated, resulting in a circuit malfunction.
For that reason, in order to increase a speed of the semiconductor
integrated circuit and improve stability of a circuit operation, in
a high-speed semiconductor integrated circuit, there is taken a
countermeasure that a decoupling capacitor with capacitance of not
less than nanofarads is inserted between a power supply and a
ground within the circuit and a current is supplied from the
decoupling capacitor against an internal rapid peak current,
thereby making it hard to generate a supply voltage drop.
[0005] As a method of forming the decoupling capacitor in the
semiconductor integrated circuit, there are a method of using a
gate oxide film of a transistor and a method of using an overlap
capacitance of interconnections or the like. In the method of using
a overlap capacitance of interconnections, the capacitance is
formed with interconnections arranged in parallel and a response
speed of the capacitance is high because of a small resistance,
whereas in order to prevent a short circuit between the
interconnections, it is necessary to increase a space between the
interconnections (interconnection space), but since the
interconnection space cannot be reduced, a capacitance value per
unit area is small, thereby making it difficult to form a capacitor
with a large capacitance. In the meantime, in the method of using a
gate oxide film of a transistor, since the gate oxide film
thickness is very thin, the capacitance value per unit area becomes
large, so that it is possible to form a capacitor having a
capacitance of nanofarads but there is a problem that a leakage
current increases or reliability decreases due to transistor
breakdown caused by ESD or the like. In FIG. 14, there is shown an
example of a structure of a decoupling capacitor using a gate oxide
film of a P-channel transistor. In FIG. 14, a gate portion 103 of
the transistor is connected to VSS 102, and a source portion 104, a
drain portion 105, and a substrate portion 106 are connected to VDD
101. Therefore, a capacitance is formed between a gate and a
channel through the gate oxide film.
[0006] Moreover, with a microfabrication of the semiconductor
integrated circuit, although a gate oxide film thickness of a
transistor has become thin and a gate length of the transistor has
become short, a supply voltage has not been reduced so as to be
proportional to it, so that a leakage current has increased. There
are three kinds of current which flow through a transistor, such as
switching current, through current, and leakage current (FIG. 15).
In FIG. 15, a switching current 201 is a current which is consumed
for the transistor to drive an interconnection or to pull up and
down a gate capacitance of the next stage, and a through current
202 is a current which flows from a P-channel transistor to an
N-channel transistor, since both the P-channel transistor and the
N-channel transistor are temporarily opened when an output signal
changes. In addition, a leakage current 203 is a current which
flows from a source to a drain, and from a gate to the drain and a
substrate, and a current which always flows even when a circuit is
not in operation.
[0007] The leakage current does not cause a problem so much in
normal operation because of its very small value compared with the
switching current or the through current. But when the circuit is
not in operation, such as in a standby mode, a lower power
dissipation is particularly required. Because neither the switching
current nor the through current flows, but the leakage current
flows, a reduction in the leakage current in the standby mode is
required. When the decoupling capacitor of not less than nanofarads
using the gate oxide film is arranged in a chip, the leakage
current due to only the decoupling capacitor will possibly be
milliamperes, and the more the decoupling capacitors are inserted
therein for a countermeasure against a supply voltage drop, the
more the leakage current increases, so a reduction in the leakage
current of the decoupling capacitor is required. As a method of
reducing the leakage current of the decoupling capacitor, there is
a method of thickening the gate oxide film, and in that case, a
reduction in capacitance per unit area due to the gate oxide film
thickness being thicker, and a reduction in capacitance due to a
decrease in a gate area of the decoupling capacitor since it is
necessity to increase a space to a transistor of a logic cell due
to a process factor or the like are caused, thereby making it
difficult to ensure sufficient capacitance.
[0008] A cell structure of the decoupling capacitor constituted so
that a leakage current may not flow in a standby mode is disclosed
in Patent Literature 1. According to this technology, by
controlling a potential provided to one electrode of the above
decoupling capacitor using an inverter, in normal operation, the
above decoupling capacitor is used as a capacitor by setting both
electrodes thereof at different potentials, and in a standby mode,
both electrodes of the decoupling capacitor are set at the same
potential so that a capacitance is not generated, thereby making a
leakage current not to flow.
[0009] A structure of the semiconductor integrated circuit for
controlling a leakage current by controlling a substrate is also
disclosed in Patent Literature 2. According to this technology, by
applying a reverse bias voltage to a substrate in a standby mode, a
threshold value of the transistor is increased, so that a drive
current of the transistor is decreased, thereby reducing a leakage
current.
[0010] It is recommended to refer to Japanese Laid-Open Patent
Application Publication No. 7-245378 as Patent Literature 1, and
the Japanese Patent Publication No. 3105512 as Patent Literature
2.
[0011] However, according to the conventional structures of the
above decoupling capacitor, it will become such a structure that a
resistance between the source and the drain of the transistor for
controlling the potential of the electrode is inserted between a
power supply of the decoupling capacitor and a ground, resulting in
a structure where a capacitor and a resistance are connected in
series. Since the resistance between the source and the drain of
the transistor has been large, when using it as the decoupling
capacitor in normal operation, there has been a problem that a
response of the capacitance has become worse.
[0012] Moreover, according to the method of reducing the leakage
current by controlling the substrate like prior art, a circuit
operation has also become worse in attempting to reduce the leakage
current of the decoupling capacitor, so that it has not been able
to gradually change a leak current value and a capacitance value
according to working speed.
SUMMARY OF THE INVENTION
[0013] The present invention is invented in order to solve such a
problem in the prior art, and the object thereof is to provide a
decoupling capacitor capable of controlling a capacitance value and
a leakage current value and also having excellent response
characteristics, and a semiconductor integrated circuit using the
same.
[0014] According to a decoupling capacitor of a first aspect of the
present invention, the decoupling capacitor comprises a MOS
transistor which has source/drain regions of a second conductive
type formed on a surface of a substrate region of a first
conductive type, wherein a capacitance value of the decoupling
capacitor is changed by changing a potential of the substrate
region.
[0015] According to this configuration, by changing the potential
of the substrate region, the capacitance value between a substrate
and a channel of the transistor changes owing to a substrate bias
effect, making it possible to change the capacitance value of the
decoupling capacitor.
[0016] According to a decoupling capacitor of a second aspect of
the present invention, in the decoupling capacitor of the first
aspect, by gradually changing the potential of the substrate
region, the capacitance value of the decoupling capacitor is
gradually changed.
[0017] According to this configuration, by gradually changing the
potential of the substrate region, the capacitance value between
the substrate and the channel of the transistor can gradually be
changed owing to the substrate bias effect, thereby making it
possible to gradually control the capacitance value of the
decoupling capacitor.
[0018] According to a decoupling capacitor of a third aspect of the
present invention, the decoupling capacitor comprises a MOS
transistor which has source/drain regions of a second conductive
type formed on a surface of a substrate region of a first
conductive type, wherein a leakage current value of the decoupling
capacitor is changed by changing a potential of the substrate
region.
[0019] According to this configuration, by changing the potential
of the substrate region, a capacitance value between a substrate
and a channel of the transistor changes owing to the substrate bias
effect, thereby making it possible to change the leakage current
value of the decoupling capacitor.
[0020] According to a decoupling capacitor of a fourth aspect of
the present invention, in the decoupling capacitor of the third
aspect, by gradually changing the potential of the substrate
region, the leakage current value of the decoupling capacitor is
gradually changed.
[0021] According to this configuration, by gradually changing the
potential of the substrate region, a capacitance between the
substrate and a channel the of transistor can gradually be changed
owing to the substrate bias effect, thereby making it possible to
gradually control the leakage current value of the decoupling
capacitor.
[0022] According to a decoupling capacitor of a fifth aspect of the
present invention, the decoupling capacitor comprises a MOS
transistor which has source/drain regions of a second conductive
type formed on a surface of a substrate region of a first
conductive type, wherein a first interconnection connected to the
substrate region and a second interconnection connected to
source/drain regions of the MOS transistor are electrically
isolated.
[0023] According to this configuration, different potentials can
easily be provided to the source/drain regions of the transistor of
the decoupling capacitor and the substrate region.
[0024] According to a decoupling capacitor of a sixth aspect of the
present invention, in the decoupling capacitor of the fifth aspect,
different potentials are provided to the first interconnection and
the second interconnection.
[0025] According to this configuration, the different potentials
can be provided to the source/drain regions of the transistor of
the decoupling capacitor and the substrate region, thereby making
it possible to reduce a leakage current owing to the substrate bias
effect.
[0026] According to a decoupling capacitor of a seventh aspect of
the present invention, in the decoupling capacitor of the fifth
aspect, the potential provided to the first interconnection is
changed by a control signal.
[0027] According to this configuration, a substrate potential
(potential of the substrate region) of the decoupling capacitor
changes according to the control signal, thereby making it possible
to control a leakage current value and a capacitance value of the
decoupling capacitor.
[0028] According to a semiconductor integrated circuit of an eighth
aspect of the present invention, the semiconductor integrated
circuit comprises: a plurality of logic cells for constituting a
logic comprising a MOS transistor which has source/drain regions of
a second conductive type formed on a surface of a first substrate
region of a first conductive type, and a MOS transistor which has
source/drain regions of a first conductivity type formed on a
surface of a second substrate region of the second conductive type,
respectively; and a decoupling capacitor comprising a MOS
transistor which has source/drain regions of the second conductive
type formed on a surface of a third substrate region of the first
conductive type, wherein an interconnection for providing a
potential to the third substrate region of the decoupling capacitor
and an interconnection for providing a potential to the
source/drain regions of the MOS transistor of the decoupling
capacitor are electrically isolated.
[0029] According to this configuration, a substrate potential of
the decoupling capacitor can be controlled independently of the
logic cell.
[0030] According to a semiconductor integrated circuit of a ninth
aspect of the present invention, in the semiconductor integrated
circuit of the eighth aspect, the third substrate region is
electrically isolated from the first substrate region.
[0031] According to this configuration, a potential different from
a substrate potential of another logic cell can be provided to the
decoupling capacitor as the substrate potential.
[0032] According to a semiconductor integrated circuit of a 10th
aspect of the present invention, in the semiconductor integrated
circuit of the eighth aspect, a potential different from that
provided to the first substrate region is provided to the third
substrate region.
[0033] According to this configuration, a potential different from
the substrate potential of another logic cell can be provided to
the decoupling capacitor as the substrate potential, and a leakage
current of the decoupling capacitor can be changed without
affecting working speed of the logic cell.
[0034] According to a semiconductor integrated circuit of an 11th
aspect of the present invention, in the semiconductor integrated
circuit of the eighth aspect, an interconnection for providing a
potential to the first substrate region of the logic cells and an
interconnection for providing a potential to the source region of
the MOS transistor which has source/drain regions of the second
conductive type of the logic cell are electrically isolated, and
the potential provided to the third substrate region of the
decoupling capacitor and the potential provided to the first
substrate region of the logic cell are controlled
independently.
[0035] According to this configuration, a potential different from
the substrate potential of another logic cell can be provided to
the decoupling capacitor as the substrate potential, and a leakage
current value of the logic cell and a leakage current value of the
decoupling capacitor can be controlled independently.
[0036] According to a semiconductor integrated circuit of a 12th
aspect of the present invention, in the semiconductor integrated
circuit of the eighth aspect, the logic cell is placed in a
plurality of cell rows, and the decoupling capacitor is placed
between the cell rows.
[0037] According to this configuration, substrate regions (well) of
the decoupling capacitor and other logic cells can easily be
separated.
[0038] According to a semiconductor integrated circuit of a 13th
aspect of the present invention, in the semiconductor integrated
circuit of the eighth aspect, the logic cell is placed in a
plurality of cell rows, the decoupling capacitor is placed in the
cell row, and the third substrate region of the decoupling
capacitor is apart from a boundary portion of the logic cell
adjacent thereto.
[0039] According to this configuration, when arranging the
decoupling capacitor in the logic cell row, other logic cells and
the substrate regions (well) of the decoupling capacitor can easily
be separated.
[0040] According to a semiconductor integrated circuit of a 14th
aspect of the present invention, in the semiconductor integrated
circuit of the eighth aspect, a potential of the third substrate
region of the decoupling capacitor is controlled according to an
operating frequency of the semiconductor integrated circuit.
[0041] According to this configuration, by providing a potential
different from that provided to the source/drain regions to the
decoupling capacitor as the substrate potential, the leakage
current value and the capacitance value of the decoupling capacitor
can be changed owing to the substrate bias effect, so that the
leakage current value and the capacitance value of the decoupling
capacitor can be changed according to the working speed.
[0042] According to a semiconductor integrated circuit of a 15th
aspect of the present invention, in the semiconductor integrated
circuit of the eighth aspect, the capacitance value of the
decoupling capacitor is controlled according to the operating
frequency of the semiconductor integrated circuit.
[0043] According to this configuration, by providing a potential
different from that provided to the source/drain regions to the
substrate potential of the decoupling capacitor, a capacitance of
the decoupling capacitor can be changed owing to the substrate bias
effect, so that it is possible to increase the capacitance in a
high operating frequency and a large supply voltage drop, and to
reduce the capacitance in a low operating frequency and a small
supply voltage drop.
[0044] According to a semiconductor integrated circuit of a 16th
aspect of the present invention, in the semiconductor integrated
circuit of the eighth aspect, the potential of the third substrate
region of the decoupling capacitor is controlled according to an
operation mode of the semiconductor integrated circuit.
[0045] According to this configuration, by providing a potential
different from that provided to the source/drain regions to the
decoupling capacitor as the substrate potential, the capacitance
value of the decoupling capacitor can be changed owing to the
substrate bias effect, so that it is possible to increase the
capacitance in an operation mode of a large supply voltage drop,
and reduce the capacitance in an operation mode of a small supply
voltage drop.
[0046] According to a semiconductor integrated circuit of a 17th
aspect of the present invention, in the semiconductor integrated
circuit of the eighth aspect, the capacitance value of the
decoupling capacitor is controlled according to an operation mode
of the semiconductor integrated circuit.
[0047] According to this configuration, by providing a potential
different from that provided to the source/drain regions to the
decoupling capacitor as the substrate potential, the leakage
current value and the capacitance value of the decoupling capacitor
can be changed owing to the substrate bias effect, so that it is
possible to increase the capacitance in an operation mode of a
large supply voltage drop, and reduce the capacitance in an
operation mode of a small supply voltage drop.
[0048] According to a semiconductor integrated circuit of an 18th
aspect of the present invention, in the semiconductor integrated
circuit of the eighth aspect, it further comprises a plurality of
functional blocks comprising a group of the logic cells, wherein
the decoupling capacitor is arranged in each of the functional
blocks, and the potential of the third substrate region of the
decoupling capacitor is controlled for every functional block
according to an operation mode of the semiconductor integrated
circuit.
[0049] According to this configuration, by providing a potential
different from that provided to the source/drain regions to the
decoupling capacitor as the substrate potential, the leakage
current value and the capacitance value of the decoupling capacitor
can be changed owing to the substrate bias effect, so that it is
possible to increase the capacitance of an internal decoupling
capacitor for a functional block with a large supply voltage drop,
and reduce the capacitance of the internal decoupling capacitor for
a functional block with a small supply voltage drop according to an
operation mode.
[0050] According to a semiconductor integrated circuit of a 19th
aspect of the present invention, in the semiconductor integrated
circuit of the eighth aspect, it further comprises a plurality of
blocks comprising a group of the logic cells, wherein the
decoupling capacitor is placed among the blocks.
[0051] According to this configuration, the leakage current value
and the capacitance value of the decoupling capacitor arranged
between blocks can also be changed.
[0052] According to a semiconductor integrated circuit of a 20th
aspect of the present invention, in the semiconductor integrated
circuit of the 19th aspect, it further comprises a plurality of
decoupling capacitors placed among the blocks, wherein respective
substrate potentials of the decoupling capacitors are controlled
independently.
[0053] According to this configuration, the leakage current value
and the capacitance value of the decoupling capacitor arranged
between the blocks can be controlled independently, and it is
possible to increase the capacitance of the decoupling capacitor
arranged near a functional block with a large supply voltage
effect, and reduce the capacitance of the decoupling capacitor
arranged near a functional block with a small supply voltage
effect.
[0054] According to a semiconductor integrated circuit of a 21st
aspect of the present invention, in the semiconductor integrated
circuit of the 20th aspect, the decoupling capacitor is arranged
also in each of the blocks, and a potential of the third substrate
region of at least one decoupling capacitor among a plurality of
decoupling capacitors arranged between the blocks is controlled in
conjunction with a control of a potential of the third substrate
region of a decoupling capacitor arranged in either of the
blocks.
[0055] According to this configuration, by achieving a commonality
of a control of the substrate potential of the decoupling capacitor
between the blocks and a control of the substrate potential of the
decoupling capacitor in the block according to an operation mode or
the like, the capacitance value of the decoupling capacitor between
the blocks can be changed in conjunction with that in the block
according to an operation mode or the like.
BRIEF DESCRIPTION OF THE DRAWINGS
[0056] FIG. 1 is a structural drawing of a decoupling capacitor
using a P-channel transistor of an embodiment of the present
invention;
[0057] FIG. 2 is a block diagram of a capacitance of the decoupling
capacitor in FIG. 1;
[0058] FIG. 3 is a structural drawing of a decoupling capacitor
using an N-channel transistor of an embodiment of the present
invention;
[0059] FIG. 4 is a view showing a layout example in the embodiment
of the present invention;
[0060] FIG. 5 is a view showing a layout example in the embodiment
of the present invention;
[0061] FIG. 6 is a view showing a layout example in the embodiment
of the present invention;
[0062] FIG. 7 is a view showing a layout example in the embodiment
of the present invention;
[0063] FIG. 8 is a view showing a layout example in the embodiment
of the present invention;
[0064] FIG. 9 is a view showing an example of a control method of
the decoupling capacitor in the embodiment of the present
invention;
[0065] FIG. 10 is a view showing an example of a control method of
the decoupling capacitor in the embodiment of the present
invention;
[0066] FIG. 11 is a view showing a layout example in the embodiment
of the present invention;
[0067] FIG. 12 is a view showing a layout example in the embodiment
of the present invention;
[0068] FIG. 13 is a view showing an example of a control method of
the decoupling capacitor in the embodiment of the present
invention;
[0069] FIG. 14 is a structural drawing of the decoupling capacitor
using a conventional gate oxide film; and
[0070] FIG. 15 is an explanatory diagram of a current flowing
through a transistor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0071] Hereafter, description will be made of embodiments of the
present invention based on the drawings.
[0072] FIG. 1 shows a structure of a decoupling capacitor in
accordance with the present invention, and reference numeral 304
represents a gate portion (gate electrode); reference numerals 305
and 306, a source portion (source region) and a drain portion
(drain region) of P type, respectively; reference numeral 307, a
substrate portion composed of an N-well (NW); reference numeral
308, a channel portion; and reference numeral 312, a gate oxide
film. This decoupling capacitor is composed of a P-channel MOS
transistor formed in an N-well (NW), and has structure of providing
VSS 302, VDD 301, and another potential NWVDD 303 different from
VDD 301 to the gate portion 304, the source portion 305 and the
drain portion 306, and the substrate portion 307, respectively.
Herein, if the potential provided to NWVDD 303 is set higher than
VDD 301, a depletion layer 309 generated in a channel portion 308
from the source portion 305 and the drain portion 306 is spread, so
that a PN junction capacitance between source/drain regions and a
substrate (NW) is reduced. Incidentally, one power supply potential
at a higher voltage supplied to a semiconductor integrated circuit
in which this decoupling capacitor is embedded represents VDD, and
the other power supply potential at a lower voltage represents VSS
(ground potential). In addition, NWVDD represents a substrate
potential of the decoupling capacitor, and is a potential provided
to the N-well (NW) in which the P-channel transistor composing the
decoupling capacitor is formed.
[0073] There is shown a structure of the capacitance of the
decoupling capacitor in FIG. 2. Herein, reference numeral 301
represents VDD; reference numeral 302, VSS; reference numeral 303,
NWVDD; reference numeral 310, a capacitance between VDD and VSS
formed by the gate oxide film 312; and reference numeral 311, a
capacitance between VDD and NWVDD formed by the depletion layer.
Herein, by providing a potential higher than VDD 301 to NWVDD 303,
the capacitance 311 between VDD and NWVDD is reduced owing to a
substrate bias effect, so a leakage current which flows from the
channel to the substrate decreases. In addition, Vt (threshold
value) goes up owing to a back bias, a leakage current which flows
from the gate to the source/drain of the transistor decreases.
Therefore, by raising the potential provided to NWVDD 303 higher
than VDD 301, the leakage current can be reduced, though the
capacitance of the decoupling capacitor is reduced. Meanwhile, if
the potential provided to NWVDD 303 is set lower than VDD 301, the
depletion layer 309 is reduced, resulting in an increase in a
capacitance between VDD and NWVDD. Herein if a forward bias is
increased, latchup will be caused and a large current will flow
through the transistor. Therefore, the potential provided to NWVDD
303 can be reduced a little bit lower than VDD 301, where latchup
will not be caused, in order that the capacitance of the decoupling
capacitor is increased.
[0074] Therefore, by changing the potential provided to NWVDD 303,
a capacitance value and a leakage current value of the decoupling
capacitor can be controlled.
[0075] While description has been made of the decoupling capacitor
composed of the P-channel MOS transistor in FIG. 1, as shown in
FIG. 3, a decoupling capacitor composed of an N-channel MOS
transistor may similarly be composed and controlled. In FIG. 3,
reference numeral 404 represents a gate portion (gate electrode);
reference numerals 405 and 406, a source portion (source region)
and a drain portion (drain region) of N type, respectively;
reference numeral 407, a substrate portion composed of an P-well
(PW); reference numeral 408, a channel portion; and reference
numeral 412, a gate oxide film. It is composed of such a structure
that VDD 402, VSS 401, and another potential PWVSS 403 different
from VSS 401 are provided to the gate portion 404, the source
portion 405 and the drain portion 406 of the transistor, and the
substrate portion 407, respectively. By providing a potential PWVSS
403 different from VSS to the substrate portion 407, a capacitance
and a leakage current can be controlled also for the decoupling
capacitor composed of the N-channel transistor. Herein, PWVSS is
the substrate potential of the decoupling capacitor, and is a
potential provided to the P-well (PW) in which the N-channel
transistor composing the decoupling capacitor is formed.
[0076] Herein, by providing a potential lower than VSS 401 to PWVSS
403, a capacitance between VSS and PWVSS is reduced owing to the
substrate bias effect, so that a leakage current which flows from
the channel to the substrate decreases. Moreover, Vt (threshold
value) goes up owing to the back bias, a leakage current which
flows from the gate to the source/drain of the transistor
decreases. Therefore, by lowering the potential provided to PWVSS
403 lower than VSS 401, the leakage current can be reduced, though
the capacitance of decoupling capacitor is reduced. Meanwhile, if
the potential provided to PWVSS 403 is set higher than VSS 401, the
depletion layer 409 is reduced, resulting in an increase in the
capacitance between VSS and PWVSS. Herein if a forward bias is
increased, latchup will be caused and a large current will flow
through the transistor. Therefore, the potential provided to PWVSS
403 can be increased a little bit higher than VSS, where latchup
will not be caused, in order that the capacitance of the decoupling
capacitor is increased.
[0077] In the case of composing the decoupling capacitor of the
N-channel transistor and composing the semiconductor integrated
circuit formed on a P-type wafer by a twin well process, because of
the P-well short-circuits, the substrate potential of the
decoupling capacitor can not be controlled. Therefore, in order to
control the substrate (potential) of the decoupling capacitor for
both of the N-channel transistor and the P-channel transistor, it
is necessary to use a triple well process. And in a twin well
process, it is necessary to use the decoupling capacitor composed
of either of the P-channel transistor or the N-channel
transistor.
[0078] Hereinafter, there are shown layout examples using the
decoupling capacitor explained above.
[0079] First, FIG. 4 shows a layout example in which the above
decoupling capacitor is arranged in a free region between cell
rows. Herein, reference numeral 501 represents a VDD power supply
strap; reference numeral 502, a VSS power supply strap; reference
numeral 503, an NWVDD power supply strap; reference numeral 504, a
decoupling capacitor composed of a P-channel transistor; reference
numeral 505, logic cells; reference numerals 506, 508, and 510,
N-wells; reference numerals 507 and 509, P-wells; reference numeral
511, a gate portion of the transistor which composes the decoupling
capacitor 504; and reference numeral 512, source/drain portions of
the transistor which composes the decoupling capacitor 504.
[0080] The gate portion 511, the source/drain portions 512, and the
substrate portion (N-well 508) of the decoupling capacitor 504 are
electrically connected to the VSS power supply strap 502, the VDD
power supply strap 501, and the NWVDD power supply strap 503,
respectively.
[0081] As for the logic cells 505, a P-well and an N-well are
arranged in an upper row and a lower row in reverse order so that
the P-wells 507 and 509 in the logic cells of the upper row and the
lower row may face each other, and the decoupling capacitor 504 is
arranged in the free region between the cell rows. For this reason,
since the N-well 508 of the decoupling capacitor 504 will touch
only to the P-wells 507 and 509 of the logic cells 505, the well of
the logic cells 505 and the well of the decoupling capacitor 504
are electrically isolated. Therefore, by providing a potential
different from that of the VDD power supply strap 501 to the NWVDD
power supply strap 503, a substrate potential of the N-well 508 of
the decoupling capacitor 504 can be provided independently of a
substrate potential of the logic cells 505.
[0082] Next, FIG. 5 shows a layout example in which the above
decoupling capacitor is arranged at the free region in the cell
row. Herein, reference numeral 601 represents VDD; reference
numeral 602, VSS; reference numeral 603, a decoupling capacitor
composed of a P-channel transistor; reference numeral 604, logic
cells; reference numeral 605, an N-well to which a substrate
potential of the decoupling capacitor is provided; reference
numeral 613, N-wells of logic cells; and reference numeral 614, a
P-well of the logic cells. The N-well 605 of the decoupling
capacitor 603 is arranged apart from a boundary of the cell, a gate
portion 606 and a source/drain portion 607 are electrically
connected to VSS 602 and VDD 601, respectively, and a substrate
potential of the transistor is supplied from a substrate power
supply pin 608. Although the well of the logic cell is generally
constituted so as to share the well with right and left cells, the
N-well 605 of the decoupling capacitor is arranged apart from a
boundary portion of the cell in this embodiment, so even when the
logic cells are arranged on right and left sides of the decoupling
capacitor, it results in a structure that the N-well of the
decoupling capacitor and the well of the logic cells are
separated.
[0083] FIG. 6 shows a layout example of a power supply
interconnection in a semiconductor in which the decoupling
capacitor of FIG. 5 is used. Herein, reference numerals 603, 609,
611 and 612 represent a decoupling capacitor, an NWVDD power supply
strap, a VDD power supply strap, and a VSS power supply strap,
respectively. Since the decoupling capacitors 603 are freely
arranged in a free region in the cell rows, positions of the power
supply pin for substrate 608 of the decoupling capacitors are not
fixed, so that an interconnections of the substrate power supply
pins 608 are difficult to be routed. For that, the NWVDD power
supply straps 609 are located at a constant spacing in advance, and
the NWVDD power supply strap 609 closest to the power supply pins
for substrate 608 of each decoupling capacitors 603 are connected
by substrate power supply lines 610, thereby making it possible to
provide the potential to the power supply pins for substrate 608.
In FIG. 6, the electrical connection is established in such a
manner that the substrate power supply lines 610 are connected from
the power supply pin for substrate 608 of each decoupling
capacitors 603 to the NWVDD power supply strap 609, so that the
potential is provided to the substrate of each decoupling
capacitors 603. In this way, the decoupling capacitors 603 can be
freely arranged at the free region in the cell rows, and as shown
in FIG. 5, since the N-well 605 of each decoupling capacitors 603
is arranged apart from the boundary of the cell, the wells of the
decoupling capacitors and the wells of the logic cells can be
electrically isolated. Moreover, by providing the potential to the
NWVDD power supply strap 609, it is possible to provide a potential
different from that to the well of the logic cells 604 to the
N-well 605 of each decoupling capacitors 603.
[0084] In FIG. 4 and FIG. 6, although description has been made of
the layout where the potential different from the power supply
potential is provided only to the substrate of the decoupling
capacitor, it is also possible to provide potentials different from
the power supply potential to the decoupling capacitor and the
logic cell, respectively. FIG. 7 shows a layout where potentials
different from the power supply potential can be provided to the
decoupling capacitor and the logic cell, respectively. Herein,
reference numeral 701 represents a VDD power supply strap;
reference numeral 702, a VSS power supply strap; reference numeral
703, an NWVDD power supply strap for decoupling capacitor;
reference numeral 704, a decoupling capacitor composed of a
P-channel transistor; reference numeral 705, logic cells; reference
numeral 706, substrate potential cells; reference numeral 707, an
NWVDD power supply strap for logic cells; and reference numeral
708, a PWVSS power supply strap for logic cells. Moreover,
reference numerals 711 and 715 represent N-wells; reference
numerals 712 and 714, P-wells; and reference numerals 713, an
N-well composing a substrate portion of the decoupling capacitor
704. A gate portion, a source portion, a drain portion, and a
substrate portion of the decoupling capacitor 704 are electrically
connected to the VSS power supply strap 702, the VDD power supply
strap 701, the VDD power supply strap 701, and the NWVDD power
supply strap 703 for decoupling capacitor, respectively, and it is
constituted in a manner similar to the decoupling capacitor 504 in
FIG. 4.
[0085] The substrate potential cells 706 are arranged in cell rows,
and in the substrate potential cells 706, the N-wells (711, 715)
and the P-wells (712, 714) thereof are electrically connected to
the NWVDD power supply strap 707 for logic cells and the PWVSS
power supply strap 708 for logic cells, respectively. In the logic
cells 705, potentials can be provided to a source region and the
substrate portion of the transistor independently, and since wells
of the substrate potential cells 706 are connected to that of the
logic cell 705, by providing a potential to the wells of the
substrate potential cells 706, the potential can be provided to the
wells of all logic cells 705 in the same row.
[0086] In FIG. 7, although description has been made of the layout
where the substrate potentials can independently be provided to the
logic cells and the decoupling capacitors, after dividing the
decoupling capacitors into two groups, such as a decoupling
capacitor group 1 and a decoupling capacitor group 2, the substrate
potential can also be independently provided to a block where the
logic cells and the decoupling capacitor group 1 are grouped, and
the decoupling capacitor group 2. FIG. 8 shows a layout
configuration of this case. In FIG. 8, reference numeral 801
represents a VDD power supply strap; reference numeral 802, a VSS
power supply strap; reference numeral 803, an NWVDD power supply
strap for decoupling capacitor; reference numeral 804, a decoupling
capacitor A arranged between cell rows; reference numeral 805,
logic cells; reference numeral 806, substrate potential cells;
reference numeral 807, an NWVDD power supply strap for logic cells;
reference numeral 808, a PWVSS power supply strap for logic cells;
reference numeral 809, a decoupling capacitors B arranged between
the cell rows. In addition, reference numerals 811 and 815
represent N-wells; reference numerals 812 and 814, P-wells;
reference numerals 813, an N-well composing a substrate portion of
the decoupling capacitor A 804. A gate portion, a source portion, a
drain portion, and a substrate portion of the decoupling capacitor
A 804 are electrically connected to the VSS power supply strap 802,
the VDD power supply strap 801, the VDD power supply strap 801, and
the NWVDD power supply strap 803 for decoupling capacitor,
respectively, and it is constituted in a manner similar to the
decoupling capacitors 504 and 704 in FIG. 4 and FIG. 7,
respectively. The substrate potential cells 806 are arranged in the
cell row, in the substrate potential cells 806, the N-well (811,
815) and P-well (812, 814) are electrically connected to the NWVDD
power supply strap for logic cells 807 and the PWVSS power supply
strap for logic cells 808, respectively, and their structure are
similar to those of the substrate potential cells 706 in FIG.
7.
[0087] The decoupling capacitors B 809 are arranged in the cell
row, and have both of the N-well and the P-well similar to the
logic cells 805, their wells are contacted to those of adjacent
logic cells, the decoupling capacitor is constituted on each well,
in the decoupling capacitors on the N-well (811, 815), a gate
portion, a source portion, a drain portion, and a substrate portion
thereof are electrically connected to the VSS power supply strap
802, the VDD power supply strap 801, the VDD power supply strap
801, and the NWVDD power supply strap 807 for logic cells,
respectively, and in the decoupling capacitors on the P-well (812,
814), a gate portion, a source portion, a drain portion, and a
substrate portion thereof are electrically connected to the VDD
power supply strap 801, the VSS power supply strap 802, the VSS
power supply strap 802, and the PWVSS power supply strap 808 for
logic cells, respectively. For that reason, since the wells of the
logic cells 805 and the decoupling capacitors B 809 are contacted
to those of the substrate potential cells 806, by providing a
potential to the wells of the substrate potential cells 806, the
potential can be provided to the wells of all the logic cells 805
and decoupling capacitors B 809 in the same row. And a substrate
potential can also be independently provided to a block where the
logic cells 805 and the decoupling capacitors B809 are grouped, and
the decoupling capacitor A 804, so that when arranging the
decoupling capacitor between the cell rows, area damage for
separating the wells can be suppressed.
[0088] In a chip, such as a microcontroller or the like, there are
a sleep mode for completely stopping its operation, a low-speed
operation mode for reducing only its operation frequency and the
like other than a normal mode for executing an instruction. Since
transistors may hardly operate in the sleep mode, there is almost
no supply voltage drop, so that the decoupling capacitor is not
required. Moreover, also in the low-speed operation mode, since the
supply voltage drop is smaller than that in normal operation, the
capacitance of the decoupling capacitor can be reduced. Moreover,
in normal operation, since the supply voltage drop is large, the
decoupling capacitors as many as possible are required. Therefore,
according to the degree of necessity of the decoupling capacitor,
in a high-speed operation, the capacitance is increased with
increasing the leakage current, and in low-speed operation, the
leakage value is reduced with reducing the capacitance, thereby
making it possible to suppress power consumption of the chip and
also stabilize operation of the chip.
[0089] Hereafter, in a semiconductor integrated circuit provided
with the decoupling capacitor according to the embodiments of the
present invention, description will be made of a configuration of
controlling the same.
[0090] First, FIG. 9 shows an example of a configuration of
controlling the above decoupling capacitor. In FIG. 9, reference
numeral 901 represents a functional block having the decoupling
capacitor therein; reference numeral 902, a substrate control
circuit; and reference numeral 903, a power supply line for
substrate for supplying the substrate potential of the decoupling
capacitor; and the substrate potential (either of NWVDD or PWVSS)
supplied by the power supply line for substrate 903 is produced
from the substrate control circuit 902, and is provided to the
substrate portion of the decoupling capacitor in the functional
block 901. Hereinafter, description will be made of an example
where the decoupling capacitor is composed of the P-channel
transistor and the NWVDD is supplied thereto as the substrate
potential.
[0091] The substrate control circuit 902 receives operation mode
signals and operating frequency signals, and when the supply
voltage drop is large, such as in a high operating frequency, a
normal operation or the like, supplies a potential the same as VDD
or a potential which are lower than VDD but higher than a potential
where latchup will be caused to the power supply line 903 for
substrate as NWVDD, and increases the capacitance value of the
decoupling capacitor. In addition, when the supply voltage drop is
small, such as in a low operating frequency, a sleep mode or the
like, it supplies a potential higher than VDD to the power supply
line for substrate 903 as NWVDD, and reduces the capacitance value
of the decoupling capacitor to reduce the leakage current.
Moreover, the potential to be supplied can gradually be changed,
and by decreasing the potential while in a large supply voltage
drop and increasing the potential while in a small supply voltage
drop, it is possible to stabilize operation of the circuit and also
control the leakage current value flowing through the circuit.
[0092] In FIG. 9, although description has been made of a case
where the circuit for controlling the substrate potential has
existed in the semiconductor integrated circuit, the control
circuit may exist outside the semiconductor integrated circuit, and
the substrate potential may be controlled from an external.
[0093] Moreover, if there are circuits which does not operate
simultaneously in the semiconductor integrated circuit, a leakage
current of a circuit which does not operate can be reduced by
controlling the substrate potential of its decoupling capacitor.
FIG. 10 shows a configuration of this case. In FIG. 10, reference
numeral 904 represents a functional block A having the decoupling
capacitor therein; reference numeral 905, a substrate control
circuit A; and reference numeral 906, a power supply line for
substrate for supplying the substrate potential of the decoupling
capacitor in the functional block A; and the substrate potential
(either of NWVDD or PWVSS) supplied by the power supply line for
substrate 906 is produced from the substrate control circuit A 905,
and is provided to the substrate portion of the decoupling
capacitor in the functional block A 904. Moreover, reference
numeral 907 represents a functional block B having a decoupling
capacitor therein; reference numeral 908, a substrate control
circuit B; and reference numeral 909, a power supply line for
substrate for supplying the substrate potential of the decoupling
capacitor in the functional block B; and the substrate potential
(either of NWVDD or PWVSS) supplied by the power supply line for
substrate 909 is produced from the substrate control circuit B 908,
and is provided to the substrate portion of the decoupling
capacitor in the functional block B 907. Hereinafter, description
will be made of an example of a case where the decoupling
capacitors in the functional block A 904 and the functional block B
907 are composed of the P-channel transistors, and NWVDD is
supplied as the substrate potential.
[0094] Herein, supposing that the functional block A 904 and the
functional block B 907 do not simultaneously operate. When the
functional block A 904 operates and the functional block B 907 does
not operate, the substrate control circuit A905 supplies a
potential the same as VDD or a potential which are lower than VDD
but higher than a potential where latchup will be caused to the
power supply line 906 for substrate as NWVDD. And the substrate
control circuit B 908 supplies a potential higher than VDD to the
power supply line for substrate 909 as NWVDD. And when the
functional block B 907 operates and the functional block A 904 does
not operate, the substrate control circuit B 908 supplies a
potential the same as VDD or a potential which are lower than VDD
but higher than a potential where latchup will be caused to the
power supply line 909 for substrate as NWVDD, and the substrate
control circuit A 905 supplies a potential higher than VDD to the
power supply line for substrate 906 as NWVDD, so that a leakage
current value of the functional block which does not operate can be
reduced.
[0095] In a chip with large scale circuits, since the degree of
complexity of a design increases, there may be a case where the
layout is made hierarchically. In that case, there are two regions,
called an intra-block and an inter-block in the layout. Meanwhile,
also when not laying out hierarchically, there may be a case where
the layout is made by placing the circuit for certain function as a
group, and also in that case, when considering a group for certain
function as a block, there may be a case where regions, called an
intra-block and an inter-block are created. When there is a region
called the inter-block like this, the decoupling capacitor can be
arranged in that portion, and by controlling the substrate
potential in a manner similar to the decoupling capacitor in the
block, the capacitance value and leakage current value can be
controlled.
[0096] FIG. 11 shows a layout example of a chip composed of a
plurality of block regions and inter-block regions. FIG. 11 shows
only a part of the chip layout. In FIG. 11, reference numerals 1001
through 1003 represent blocks, and reference numeral 1004
represents decoupling capacitors arranged in an inter-block region.
Herein, since the decoupling capacitors 1004 are arranged between
the blocks, in order to provide a potential to the well different
from that of the block region, it is easy to electrically isolate
the wells. By using another power supply as a substrate potential
of the decoupling capacitors 1004 arranged between blocks, a
capacitance value and a leakage current value of the decoupling
capacitors 1004 between the blocks can be controlled.
[0097] In FIG. 11, although description has been made of the
example where the decoupling capacitors has been arranged between
the blocks as one group, it maybe arranged as a plurality of
groups. FIG. 12 shows an example where the decoupling capacitors in
an inter-block region are split into a plurality of groups. In FIG.
12, reference numerals 1101 through 1103 represent blocks, and
reference numerals 1104 through 1106 represent decoupling
capacitors arranged in an inter-block region. The decoupling
capacitors A 1104, the decoupling capacitors B 1105, and the
decoupling capacitors C 1106 are obtained by respectively grouping
decoupling capacitors in the vicinity of the block A 1101, block B
1102, and block C 1103, respectively. In general, a decoupling
capacitor which is arranged in the vicinity closer to a location
where a supply voltage drop is generated has a higher supply
voltage drop suppression effect, and since a larger capacitance
value of the decoupling capacitor A 1104 maybe more effective for
the supply voltage drop suppression effect for the block A 1101,
when a supply voltage drop of the block A 1101 is large, the
capacitance value of the decoupling capacitor A 1104 is increased
to supress supply voltage drop effectively, whereas when the supply
voltage drop of the block A 1101 is small, the capacitance value of
the decoupling capacitors A 1104 is reduced to reduce a leakage
current, thereby enabling to effectively use the decoupling
capacitors.
[0098] In FIG. 12, although neighboring decoupling capacitors are
grouped for every block, it is not necessary to make the number of
the groups coincide with the number of blocks. For example, when
the supply voltage drop of the block A 1101 is larger than that of
another blocks, the decoupling capacitors A and the decoupling
capacitors C may also be grouped into a group of decoupling
capacitors, or the like. Moreover, although the capacitance value
of the decoupling capacitors may be changed corresponding to a
block in the vicinity of the group of the decoupling capacitor, it
is not necessary to make it correspond to the neighboring
block.
[0099] Further, as shown in FIG. 12, by achieving a commonality of
a control of a substrate potential of each decoupling capacitor
arranged between the blocks with a control of a substrate potential
of the decoupling capacitor arranged in each block, the decoupling
capacitor can be used more effectively. FIG. 13 shows an example of
a configuration of controlling the decoupling capacitor in this
case. In FIG. 13, reference numerals 1201, 1205, and 1209 represent
blocks A, B, and C having decoupling capacitors therein,
respectively, reference numerals 1204, 1208, and 1212 represent
decoupling capacitors A, B, and C arranged between the blocks,
respectively, reference numerals 1202, 1206, and 1210 represent
substrate control circuits A, B, and C, respectively, and reference
numerals 1203, 1207, and 1211 represent power supply lines for
substrate. The power supply line 1203 for substrate is provided
from the substrate control circuit A 1202, and is connected to both
of a substrate potential of the decoupling capacitor in the block A
1201 and a substrate potential of the decoupling capacitor A 1204
between the blocks. Herein, supposing that both of the decoupling
capacitors arranged in the blocks and between the blocks are
composed of the P-channel transistors, the substrate control
circuit A 1202 receives operation mode signals and operating
frequency signals, when the supply voltage drop is large, such as
in a high operating frequency, a normal operation or the like,
supplies a potential the same as VDD or a potential which are lower
than VDD but higher than a potential where latchup will be caused
to the power supply line 1203 for substrate to thereby increase
capacitance values of the decoupling capacitors in the block A 1201
and the decoupling capacitors A 1204 between the blocks. Meanwhile,
when the supply voltage drop is small, such as in a low operating
frequency, a sleep mode or the like, it provides a potential higher
than VDD to the power supply line 1203 for substrate, and reduces
the capacitance values of the decoupling capacitors in the block A
1201 and the decoupling capacitors A 1204 between the blocks to
thereby reduce a leakage current. In addition, the potential to be
supplied can gradually be changed, and by decreasing the potential
in a large supply voltage drop and increasing the potential in a
small supply voltage drop, it is possible to stabilize operation of
the circuit and also control the leakage current value flowing
through the circuit. Herein, the capacitance value of the
decoupling capacitors A 1204 between the blocks can be changed in
conjunction with the capacitance value of the decoupling capacitors
in the block A1201. Further, a control in a manner similar to these
is performed to the functional block B 1205 and the decoupling
capacitors B 1208 by the substrate control circuit B 1206, and also
to the functional block C 1209 and the decoupling capacitors C 1212
by the substrate control circuit C 1210, so that it is possible to
control the decoupling capacitors in the block and the decoupling
capacitors between the blocks effectively.
[0100] In FIG. 13, although the power supply lines 1203, 1207, and
1211 for substrate are made in common, not the power supply lines
for substrate but signal lines for control may be made in common,
and the power supply lines for substrate may be separated into two,
one is for the intra-block and the other is for the inter-block. In
addition, although all controls of the decoupling capacitors in the
block and between the blocks are made in common, only a part of
combination thereof may be made in common.
[0101] Moreover, as shown in FIG. 11, even when decoupling
capacitors 1004 are arranged between the blocks, the control of the
substrate potential of the decoupling capacitors 1004 may be made
in common to the control of the substrate potential of the
decoupling capacitors arranged in either of the blocks A 1001, B
1002, and C 1003.
[0102] Incidentally, in the explanation of the control other than
FIG. 3 so far, although description has mainly been made a case
where the decoupling capacitors has been composed of the P-channel
MOS transistors, in either examples after FIG. 4, the decoupling
capacitors may also be composed of the N-channel MOS
transistors.
[0103] According to the decoupling capacitor of the present
invention, the capacitance value and the leakage current value
thereof can be controlled, and it is useful to semiconductor
integrated circuits or the like embedded this decoupling
capacitor.
* * * * *